Example 7.19 (a) 1 kg water at 0°C is brought into contact with a heat reservoir at 90°C. When water has reached 90°C, find (i) Entropy change of water, (ii) Entropy change of the reservoir, (iii) Entropy change of the universe. (b) If water is heated from 0°C to 90°C by first bringing it in contact with the reservoir at 40°C and then with a reservoir at 90°C, what will be the entropy change of the universe? (c) Explain how water might be heated from 0°C to 90°C with almost no change in entropy of the universe?